Recently so-called "keyless" printing machines, which have no buttons to operate in order to control the ink-supplying rate, have been used in place of conventional printing machines which have a number of ink-supply control buttons. Because of this, conventional machines usually require a skilled operator to control the ink supply rate paper to the ink transfer rollers such that a sheet paper is printed with a uniform density. This is partly because the keyless printing machine is less expensive than the conventional one, and partly because no skilled labor is required to operate the keyless printing machine.
The keyless printing machine will be described, with reference to FIG. 1.
As is shown in FIG. 1, the keyless printing machine comprises ink pan 1 containing ink 2, and an ink fountain roller 4 with its lower part immersed in ink 2. The machine further comprises anilox roller 5 located above ink fountain roller 4 and contacting therewith, doctor blade 6 arranged in contact with anilox roller 5, plate cylinder 7 provided above anilox roller 5, and two inking rollers 8 each arranged in contact with roller 5 and plate cylinder 7.
Ink fountain roller 4 is rotated, thereby to transfer ink from ink pan 1 onto anilox roller 5. Doctor blade 6 is operated to remove an excess of ink 2 from anilox roller 5. Thus, an appropriate amount of ink is transferred from roller 5 onto both inking rollers 8 as roller 5 rotates in contact with inking rollers 8. Inking rollers 8 transfers ink 2 onto plate cylinder 7 as rollers 8 rotate in contact with plate cylinder 7.
Anilox roller 5 comprises a core roller (not shown) and a matrix layer (not shown, either) formed on the periphery of the core roller. The matrix layer is made of either ceramics (e.g., alumina ceramics or tungsten carbide) or a soft metal. A number of patterned cells or depressions 5a, which are quadrangular pyramid-shaped as is shown in FIG. 2B, are made in the surface of the layer as is illustrated in FIG. 2A. Alternatively, a number of cells 5b, which are shaped like quadrangular frustrum pyramid shaped as is shown in FIG. 3B, are made in the surface of the matrix layer as is illustrated in FIG. 3A. These cells 5a or 5b are formed by applying a laser beam onto the layer when the layer is made of ceramics, or by rolling a matrix roll, which has a number of projections, on the layer when the later is made of a soft metal. This anilox roller acts as ink metering and transfer roller.
The conventional keyless printing machine and anilox roller have the following drawbacks.
(1) The machine is expensive when the cell of anilox roller 5 are formed by means of a special apparatus such as a laser.
(2) The cell may have different sizes when formed by means of a laser, due to changes in the intensity of the laser beam emitted by the laser. The cell may have different shapes when formed by means of a matrix roll. In either case, the machine cannot print a sheet of paper in an uniform density.
(3) As the outer layer of the anilox roller is worn by the doctor blade, the shapes of the cells will change. Hence, the lifetime of the roller is short.
Accordingly it is the object of the present invention to provide an inking unit which has an anilox roller always having spherical cells in its periphery even if the periphery is worn, and which is inexpensive, and which has a long lifetime, and also to provide a method of manufacturing this inking unit.